Ground fault interrupt circuit for electric vehicle

ABSTRACT

In one implementation, a ground fault interrupt circuit is provided for a utility power connection to an electric vehicle charging unit. The ground fault interrupt circuit may include a gain amplifier having an input connected to be capable of receiving a differential current from a current sensing transformer and a comparator having an input connect to a reference voltage. It includes a rectifier circuit connected between the gain amplifier and the comparator with a charge accumulator circuit coupled between the rectifier and the comparator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/US2011/032576 by Flack et al.,entitled GROUND FAULT INTERRUPT CIRCUIT FOR ELECTRIC VEHICLE, filed on14 Apr. 2011, herein incorporated by reference in its entirety, whichclaims the benefit of the following U.S. Provisional PatentApplications, which are herein incorporated by reference in theirentireties:

U.S. Provisional Application 61/324,296, by Albert Flack, filed 14 Apr.2010, entitled GROUND FAULT INTERRUPT CIRCUIT FOR ELECTRIC VEHICLE; U.S.Provisional Application 61/374,612, Albert Flack, filed 18 Aug. 2010,entitled GROUND FAULT INTERRUPT AUTOMATIC TEST METHOD FOR ELECTRICVEHICLE; and

U.S. Provisional Application 61/324,293, by Albert Flack, filed 14 Apr.2010, entitled PILOT SIGNAL GENERATION CIRCUIT.

BACKGROUND

One way to charge an electric vehicle is to supply the vehicle withpower so that a charger in the vehicle can charge the battery in thevehicle. If there is a ground fault in the electrical system in the carand someone is touching car while grounded, that person could beshocked.

What is needed to avoid this situation is a ground fault interrupt orGFI circuit to disconnect the power to the vehicle if a ground fault isdetected.

SUMMARY

In one implementation, a ground fault interrupt circuit is provided fora utility power connection to an electric vehicle charging unit. Theground fault interrupt circuit may include a gain amplifier having aninput connected to be capable of receiving a differential current from acurrent sensing transformer and a comparator having an input connect toa reference voltage. It includes a rectifier circuit connected betweenthe gain amplifier and the comparator with a charge accumulator circuitcoupled between the rectifier and the comparator.

Some embodiments may include an inverter between the gain amplifier andthe charge accumulator circuit.

In one possible implementation, a GFI circuit is provided for a utilitypower connection to an electric vehicle charging unit. The GFI circuitincludes a gain amplifier having an input connected to be capable ofreceiving a differential current from a current sensing transformer. Afilter is connected to an output of the gain amplifier. In variousembodiments the filter is a half wave rectified dual stage filter. Acomparator is connected to an output of the filter. The output of thecomparator is connected to a latching circuit. A contactor controlcircuit is connected to the output of the fault latch. The contactorcontrol circuit may include a contactor control relay. The output of thecontactor control circuit is connected to a utility power line contactorso as to be capable of connecting/disconnecting utility power. Invarious embodiments, a microprocessor is connected to a reset input ofthe fault latch.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will be betterunderstood with regard to the following description, appended claims,and accompanying drawings where:

FIG. 1 shows a schematic view of a cable to connect utility power to anelectric vehicle (not shown) along with some associated circuitry.

FIG. 2 shows an enlarged view schematic drawing of the GFI circuit ofFIG. 1.

FIG. 3 shows a schematic view of a contactor control circuit.

FIG. 4 shows an enlarged more complete schematic of the pilot circuitryshown in partial schematic in FIG. 1.

FIG. 5 is a partial schematic showing a microprocessor, which may beused to govern the output of the GFI circuit.

FIG. 6 shows a simplified plot of an example of possible chargeaccumulation by the double stage filter leading to a fault detection bythe comparator.

FIG. 7 shows a schematic view of an alternate embodiment of a portion ofthe GFI circuit of FIG. 2.

DESCRIPTION

FIG. 1 shows a schematic view of a cable 100 to connect utility power toan electric vehicle (not shown) along with some associated circuitry. Inthe embodiment of FIG. 1, the cable 100 contains L1 and L2 and ground Glines. The cable 100 connects to utility power at one end 100 u and toan electric vehicle (not shown) at the other end 100 c. The electricvehicle (not show) could have an onboard charger, or the electricvehicle end 100 c of the cable 100 could be connected to a separate,optionally free standing, charger (not shown). The separate charger (notshown) would in turn be connected to the electric vehicle for chargingonboard batteries, or other charge storage devices. In other embodimentsnot shown, a charger could be integrated into the cable 100.

The cable 100 contains current transformers 110 and 120. The currenttransformer 110 is connected to a GFI circuit 130 which is configured todetect a differential current in the lines L1 and L2 and indicate when aground fault is detected. Contactor 140 may be open circuited inresponse to a detected ground fault to interrupt utility power fromflowing on lines L1 and L2 to the vehicle (not shown).

FIG. 2 shows an enlarged view schematic drawing of the GFI circuit 130of FIG. 1. In the embodiment of FIG. 2, the GFI circuit 130 is designedto trip in the 5-20 mA range for GFI in accordance with the UL 2231standard.

A signal provided by current transformer 110 (FIG. 1) at pins 3 and 4 ofthe GFI circuit 130 is amplified by op amp 132 to a voltage reference.That voltage reference is filtered by a double stage RC filter 134 toeliminate spurious noise spikes.

Fault current detected by current transformer 110 (FIG. 1) is convertedto voltage by gain amplifier 134 for comparison by comparator 136. Theoutput of the gain amplifier 132 is filtered prior to being supplied tothe comparator 136 with the double stage RC filter 134 to removespurious noise that could cause nuisance shut downs. Output ofcomparator 136 is latched with flip-flop 138 so that contactor 140(FIG. 1) does not close after a fault has been detected. The comparator136 provides a GFI_TRIP signal output, which is an input to the faultlatch 138 to produce a latched GFI_FAULT signal.

The double stage filter 134 provides a delay so that the shut-offcircuit does not immediately shut off if a fault is detected. The doublestage filter 134 is a half-wave rectified circuit that allows anincoming pulse width that is less than 50% in some embodiments, or evenas small as about 38% in some embodiments, to accumulate over time sothat it will charge at a faster rate than it discharges. The doublestage filter 134 accumulates charge and acts as an energy integrator.Thus, the GFI circuit 130 waits a time period before causing shut down.This is because it is not desirable to have an instantaneous shut downthat can be triggered by noise in the lines L1 or L2, or in the GFIcircuit 130. The GFI circuit 130 should trip only if a spike has somepredetermined duration. In the embodiment shown, that duration is one totwo cycles.

The filter 134 charges through R102 and R103. When it discharges, itonly discharges through R102, so it charges more current than itdischarges over time. The double stage filter 134 is a half waverectified circuit due to diode D25.

Diodes D4 provide surge suppression protection. In typical embodiments,the gain amplifier 132 may actually have surge suppression protection.Despite this, diodes D4 are added to provide external redundantprotection to avoid any damage to the gain amplifier 132. This redundantprotection is significant, because if the gain amplifier 132 is damaged,the GFI protection circuit 130 may not function, resulting in inadequateGFI protection for the system. For example, without the redundant surgesuppressing diodes D4, if a power surge were to damage the gainamplifier 132 so that it no longer provided output, the GFI circuit 130would no longer be able to detect faults. Since UL 2231 allows utilitypower L1 and L2 power to be reconnected after a GFI circuit detects aground fault surge, utility power L1 and L2 could conceivably bereconnected after the gain amplifier 132 had been damaged. It issignificant to note that the diodes D4 are connected to the upper andlower reference voltage busses of the circuit, i.e. ground and 3 volts,respectively, so that they can easily dissipate surge current withoutcausing damage to the circuitry. Thus, the redundant surge suppressiondiodes D4 provide an additional safety feature for the GFI protectioncircuit 130.

FIG. 3 shows a schematic view of a contactor control circuit 170. Thecontactor control circuit 170 opens/closes the contactor 140 (FIG. 1) todisconnect/connect the utility power L1 and L2 from/to the vehicleconnector 100 c. As discussed above with reference to FIG. 2, theGFI_TRIP signal is output by the comparator 136 and is an input to thefault latch 138 to produce the GFI_FAULT signal. The GFI_FAULT signaloutput by the fault latch 138 is an input to the contactor controlcircuitry 170, shown in FIG. 3, used to control the contactor controlrelay K1. The contactor control relay K1 is used to open/close thecontactor 140 (FIG. 1) to disconnect/connect the utility power L1 and L2from/to the vehicle connector 100 c. The CONTACTOR_AC signal output bythe contactor control relay K1 is connected to the contactor coil 141(FIG. 1) through pin 1 of the connector 181 (FIG. 1) associated with theutility present circuitry 180 (FIG. 1).

The GFI_TRIP signal output by the comparator 136 (FIG. 2) is not onlyprovided to the contactor control circuit 170 (FIG. 3), but also isprovided as an input to the contactor disable latch 152, shown in FIG. 4to produce a CONTACTOR_FAULT_DISABLE signal. FIG. 4 shows an enlargedmore complete schematic view of the pilot circuitry 150 shown in partialschematic in FIG. 1. Additionally, the contactor disable latch 152 (FIG.4) is an input to the contactor control circuitry 170 (FIG. 3) tocontrol the contactor control relay K1 (FIG. 3). TheCONTACTOR_FAULT_DISABLE signal is used to open the contactor controlrelay K1 (FIG. 3), which opens the contactor 140 (FIG. 1) to opencircuit/close circuit the utility power L1 and L2. This provides aredundant circuit for this important safety control circuit. Further, itrequires the reset of both latches 138 (FIG. 2) and 152 (FIG. 4) toreconnect L1 and L2 utility power to the vehicle connector 100 c. Thisprovides further software redundancy for this important safety controlcircuit.

FIG. 5 is a partial schematic showing a microprocessor 500, which may beused to govern the output of the GFI circuit 130 (FIG. 2). Referring toFIGS. 2 and 5, the GFI_FAULT output signal from the fault latch 138 isprovided as an input at pin 552 to the microprocessor 500. Themicroprocessor 500 outputs at pin 538 the GFI_RESET signal to the GFIcircuit 130 to control the reset of the GFI_circuit 130, in accordancewith a predetermined standard, such as UL 2231. This may be accomplishedby outputting the GFI_RESET signal to the fault latch 138, and to theCONTACTOR_RESET to the contactor disable latch 152 (FIG. 4).

Also, the microprocessor 500 may also output at pin 81 the GFI_TESTsignal, which causes a GFI test circuit 139 to simulate a ground faultfor testing the functionality of the contactor 140 (FIG. 1). The GFItest circuit 139 output AC_1 provides a path via pin 2 of the connector181 to the contactor coil 141 (FIG. 1) to exercise the contactor 140.

Additionally, the microprocessor 500 provides a CONTACTOR_CLOSE signaloutput to the contactor close circuit to close the contactor controlrelay K1 (FIG. 3).

FIG. 6 shows a simplified plot 600 of an example of possible chargeaccumulation by the double stage filter 134 (FIG. 2) leading to a faultdetection by the comparator 136 (FIG. 2). Referring to FIGS. 2 and 6,since the double stage filter 134 discharges slower than it charges,several successive current pulse detections 601, 602, and 603 would berequired to cause sufficient charge to accumulate a voltage level thatwould cause the comparator to indicate a GFI_TRIP. Thus, faults byspurious noise can be minimized. In this simplified example plot, a 1.5volts pulse of about 38% of the duty cycle for three successive cyclescauses sufficient charge to accumulate a GFI TRIP signal. Otherembodiments are possible by appropriate selection of the R102, R103, andC51.

FIG. 7 is shows a schematic view of an alternate embodiment 730 of aportion of the GFI circuit 130 of FIG. 2. In this embodiment, the input730 i of the GFI circuit 730 is connected to gain amplifier 732 via anoptional EMI protection circuit 731. Thus, the signal provided by thecurrent transformer 110 is passed through the EMI protection circuit731, which includes series inductor L7 and resistor R71, of about 50microHenries and 50 ohms, respectively, with capacitors C34, C33, C20,each about 0.001 microFarads, coupled across the differential input 730i and coupled to ground.

Further, in this embodiment, the input 730 i is connected to theamplifier 732 via a series capacitor C17, of about 10 microFarads, andseries resistor R23 (about 50 ohms) to the inverting input of theamplifier 732. The non-inverting input of the operational amplifier 732is referenced to 1.5 volts. The output of the amplifier 732 is feed backto the inverting input of amplifier 732 via parallel coupled feedbackresistor R24 and an optional feedback capacitor C15, of about 50K ohmsand 0.01 microFarads respectively. The optional capacitor C15 providesfiltering to reduce noise. The output of the amplifier 733 is providedto the inverting input of amplifier 733 via resistor R18 (about 10Kohms). The non-inverting input of the amplifier 733 is supplied thereference voltage of 1.5 volts. The output of the amplifier 733 is feedback via resistor R15 (about 10K ohms). Thus, the amplifier 733 has again of unity so merely provides an inverted output from that of thegain amplifier 732.

As such, the series capacitor C17 passes the AC portion of thedifferential current input 730 i, which is both positive and negative.The input 730 i is referenced to 1.5V by the gain amplifier 732. Theoutput of the gain amplifier 732 is inverted by the inverting amplifier733.

The output of the amplifier 732 and the output of the amplifier 733 areconnected by diodes D2 and D1, respectively, to the charge accumulator734. The diodes D2 and D1 provide a full wave rectified output (withrespect to 1.5V) to the charge accumulator 734. The anode of diode D2and the anode of diode D1 form a full wave rectifier circuit and areconnected to sum at the input of the charge accumulator 734. The cathodeof diode D2 is connected to the output of gain amplifier 732 and thecathode of the diode D1 is connected to the output of the invertingamplifier 733. Thus, in this case, as used herein, the chargeaccumulator 734 actually “accumulates” depleted charge.

The charge accumulator 734 includes a series connected resistor R10 ofabout 25 k ohms, connected between the diodes D2 and D1 and thenon-inverting input of comparator 736. The charge accumulator 734further includes resistor R7, of about 1M ohm, connected between thereference voltage 1.5V and the non-inverting input to the comparator736. A capacitor C1, of about 0.1 microFarad is connected between thenon-inverting input of the comparator 736 and ground.

A reference voltage of 0.5 volts is provided to the inverting input ofthe comparator 736 by the R72 and R73 voltage divider. The resistor R72,of about 20K ohms, is connected between the reference 1.5V and theinverting input of the comparator 736. The resistor R73, about 10K ohmsis connected between the inverting input of the comparator 736 andground.

The output of the comparator 736 may be supplied directly/indirectly tothe microprocessor 500 (FIG. 5), latch 138 (FIG. 2) or/and latch 152(FIG. 4), such as discussed above with reference to FIGS. 2-5.

It is worthy to note that any reference to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment may beincluded in an embodiment, if desired. The appearances of the phrase “inone embodiment” in various places in the specification are notnecessarily all referring to the same embodiment.

The illustrations and examples provided herein are for explanatorypurposes and are not intended to limit the scope of the appended claims.This disclosure is to be considered an exemplification of the principlesof the invention and is not intended to limit the spirit and scope ofthe invention and/or claims of the embodiment illustrated.

Those skilled in the art will make modifications to the invention forparticular applications of the invention.

The discussion included in this patent is intended to serve as a basicdescription. The reader should be aware that the specific discussion maynot explicitly describe all embodiments possible and alternatives areimplicit. Also, this discussion may not fully explain the generic natureof the invention and may not explicitly show how each feature or elementcan actually be representative or equivalent elements. Again, these areimplicitly included in this disclosure. Where the invention is describedin device-oriented terminology, each element of the device implicitlyperforms a function. It should also be understood that a variety ofchanges may be made without departing from the essence of the invention.Such changes are also implicitly included in the description. Thesechanges still fall within the scope of this invention.

Further, each of the various elements of the invention and claims mayalso be achieved in a variety of manners. This disclosure should beunderstood to encompass each such variation, be it a variation of anyapparatus embodiment, a method embodiment, or even merely a variation ofany element of these. Particularly, it should be understood that as thedisclosure relates to elements of the invention, the words for eachelement may be expressed by equivalent apparatus terms even if only thefunction or result is the same. Such equivalent, broader, or even moregeneric terms should be considered to be encompassed in the descriptionof each element or action. Such terms can be substituted where desiredto make explicit the implicitly broad coverage to which this inventionis entitled. It should be understood that all actions may be expressedas a means for taking that action or as an element which causes thataction. Similarly, each physical element disclosed should be understoodto encompass a disclosure of the action which that physical elementfacilitates. Such changes and alternative terms are to be understood tobe explicitly included in the description.

Having described this invention in connection with a number ofembodiments, modification will now certainly suggest itself to thoseskilled in the art. The example embodiments herein are not intended tobe limiting, various configurations and combinations of features arepossible. As such, the invention is not limited to the disclosedembodiments, except as required by the appended claims.

What is claimed is:
 1. A ground fault interrupt circuit for a utilitypower connection to an electric vehicle charging unit, the ground faultinterrupt circuit comprising: a) a gain amplifier having an inputconnected to be capable of receiving a differential current from acurrent sensing transformer; b) a filter having an input connected to anoutput of the gain amplifier; c) a comparator having an input connectedto an output of the half wave rectified dual stage filter; d) a faultlatch having an input connected to the output of the comparator; e) acontactor control circuit having an input connected to an output of thefault latch; and f) a utility power line contactor having a contactorcontrol input connected to an output of the contactor control circuit.2. The circuit of claim 1, wherein the filter is a half wave rectifieddual stage filter.
 3. The circuit of claim 1, wherein the gain amplifiercomprises a surge protection circuit, and further comprising a redundantsurge protection circuit connected to an input of the gain amplifier. 4.The circuit of claim 3, wherein the redundant surge protection circuitcomprises a pair of diodes connected to lower and upper referencebusses.
 5. The circuit of claim 1, further comprising a microprocessorconnected to the output of the fault latch so as to detect a fault trip,and to a fault latch reset input of the fault latch.
 6. The circuit ofclaim 1, wherein the contactor control circuit further comprises acontactor control relay, the contactor control relay is connected to theutility power line contactor.
 7. The circuit of claim 6, furthercomprising a contactor disable latch responsive to the output of thecomparator, the contactor disable latch being connected to an input ofthe contactor control circuit in parallel with the output of fault latchso as to provide a redundant control signal for controlling thecontactor control relay.
 8. The circuit of claim 1, further comprising adifferential current sensing transformer coupled to utility power lines.9. A method for electric vehicle charging for detecting a ground faultcomprising: detecting a differential current in utility power supply;generating a ground fault signal from the detected differential current;accumulating the ground fault signal over time; and comparing theaccumulated ground fault signal to a threshold voltage; and causing aground fault interrupt when the accumulated ground fault signal exceedsthe threshold voltage.
 10. The method of claim 9, wherein accumulatingthe ground fault signal over time comprises filtering the ground faultsignal.
 11. The method of claim 10, wherein filtering the ground faultsignal comprises using a double stage filter.
 12. The method of claim11, wherein filtering the ground fault signal comprises using a halfwave rectifying double stage filter.
 13. The method of claim 9, whereinaccumulating the ground fault signal over time comprises accumulatingground fault signals having a voltage level below the threshold voltageso as to cause the ground fault interrupt at the threshold voltage. 14.The method of claim 9, wherein accumulating the ground fault signal overtime comprises accumulating multiple discrete signals having a voltagelevel below the threshold voltage so as to cause the ground faultinterrupt at the threshold voltage.
 15. The method of claim 14, whereinaccumulating the ground fault signal over time and causing the groundfault interrupt comprises causing the ground fault interrupt when themultiple discrete signals have a duration that is less than a dutycycle.
 16. The method of claim 9, wherein generating the ground faultsignal from the detected differential current comprises using a gainamplifier.
 17. The method of claim 9, comprising latching a ground faultinterrupt signal when the accumulated ground fault signal exceeds thethreshold voltage.
 18. The method of claim 9, comprising opening autility power line contactor when the accumulated ground fault signalexceeds the threshold voltage.
 19. The method of claim 9, furthercomprising generating an inverted ground fault signal, and whereinaccumulating further comprises accumulating both the ground fault signaland the inverted ground fault signal over time.
 20. The method of claim19, further comprising rectifying and the ground fault signal and theinverted ground fault signal prior to accumulating.
 21. The method ofclaim 19, wherein generating the ground fault signal comprisesgenerating the ground fault signal about a reference voltage, andwherein generating the inverted ground fault signal comprises generatingthe ground fault signal about the reference voltage.
 22. The method ofclaim 21, further comprising rectifying and the ground fault signal andthe inverted ground fault signal prior to accumulating.
 23. A method forelectric vehicle charging for detecting a ground fault comprising:detecting a differential current in utility power supply; generating aground fault signal from the detected differential current; filteringthe ground fault signal; and comparing the filtered ground fault signalto a threshold voltage; and disconnecting the utility power supply whenthe filtered ground fault signal exceeds the threshold voltage.
 24. Themethod of claim 23, wherein filtering the ground fault signal comprisesusing a half wave rectifying double stage filter.
 25. The method ofclaim 23, comprising generating a latched fault signal when the filteredground fault signal exceeds the threshold voltage.
 26. The method ofclaim 25, comprising opening a utility power contactor to disconnect theutility power supply in response to the latched fault signal.
 27. Themethod of claim 26, wherein generating the latched fault signalcomprises generating a ground fault interrupt fault signal andgenerating a contactor fault disable signal, and further comprisingopening the utility power contactor in response to either the groundfault interrupt fault signal or the contactor fault disable signal. 28.A ground fault interrupt circuit for a utility power connection to anelectric vehicle charging unit, the ground fault interrupt circuitcomprising: a) a gain amplifier having an input connected to be capableof receiving a differential current from a current sensing transformer;b) a comparator having an input connect to a reference voltage; c) arectifier circuit connected between the gain amplifier and thecomparator; and d) a charge accumulator circuit coupled between therectifier and the comparator.
 29. The circuit of claim 28 furthercomprising an inverter connected between the gain amplifier and therectifier circuit.
 30. The circuit of claim 28, further comprising aninverter having an input connected to an output of the gain amplifier,and wherein the rectifier circuit is a full wave rectifier circuitconnected to the output of the gain amplifier and to an output of theinverter, and wherein an output of the full wave rectifier circuit isconnected to the charge accumulator circuit.
 31. The circuit of claim28, wherein the charge accumulator comprises the rectifier circuit, andwherein the rectifier circuit is a half wave rectifier circuit connectedto the gain amplifier.
 32. The circuit of claim 28 further comprising anEMI protection circuit at an input of the ground fault interruptcircuit.
 33. The circuit of claim 32 wherein the EMI protection circuitcomprises an inductor and a resistor connected in series, and at leastone capacitor connected across the differential input and to ground. 34.The circuit of claim 28 further comprising a fault latch having an inputconnected to an output of the comparator.
 35. The circuit of claim 34further comprising a contactor control circuit having an input connectedto an output of the fault latch.
 36. The circuit of claim 35, furthercomprising a utility power line contactor having a contactor controlinput.
 37. The circuit of claim 36 further comprising an inverter havingan input connected to an output of the gain amplifier, and wherein therectifier circuit is a full wave rectifier circuit connected to theoutput of the gain amplifier and to an output of the inverter, andwherein an output of the full wave rectifier circuit is connected to thecharge accumulator circuit.
 38. The circuit of claim 36, wherein thecharge accumulator comprises the rectifier circuit, and wherein therectifier circuit is a half wave rectifier circuit connected to the gainamplifier.